SANTA ROSA (CBS SF) — Sonoma County health officials said Tuesday they were concerned by the mosquito breeding threat posed by backyard pools in homes that were destroyed in this month’s devastating wildfire outbreak.

Marin/Sonoma Mosquito & Vector Control District officials said they had begun mosquito surveillance and control work in residential areas affected by the recent fires.

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“Currently our main concern is spas and swimming pools that can produce tens of thousands of mosquitoes if left unmaintained,” said Jason Sequeira, Field Supervisor for the Marin/Sonoma Mosquito and Vector Control District, in a news release. “Areas found producing mosquitoes will be treated with environmentally compatible materials, documented, and monitored.”

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The fires destroyed approximately 7,400 structures across the wine country with the majority of those buildings being homes.

Vector control technicians said they have identified nearly 200 new sources of mosquito production, consisting mostly of swimming pools in burn areas. But spas and exposed septic tanks also posed problems.

Officials said they have started to receive calls from residents affected by the fires reporting areas that are producing mosquitoes on their properties.

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In the days prior to the fires, district officials reported two birds infected by the West Nile virus had been discovered in the vicinity of Stanford Ct. and Princeton Ave. in Sonoma.